Chapter 52: Population Ecology(Final check at 9:00 AM 12/11/10. Looks complete.) Population: a group of individuals of a single species living in the same general area Population ecology: the study of populations and how the environment influences that population’s density, distribution, size, and age structure.
Section 52.1:Dynamic Biological Processes influence population’s density, dispersion, and demography
Density [number of individuals per capita] (Eg: number of oak trees per kilometer) - Mark-recapture method: captured animals are marked with tags, collars, bands, or spots of dyes, and then released; after a few days or weeks, traps are set again; the second capture yields both marked and unmarked individuals. Data yields researches to estimate the total number of individuals in the population. Dispersion [How individuals space/pattern themselves in a certain population] - Immigration: an influx of organisms entering a certain environment - Emigration: an influx of organisms leaving a certain environment - Territoriality: the defense of a physical space [Insert figure 52.3 from textbook] Demography [the study of vital statistics of a population] - Life table: presents age-specific survival data for a population - Survivorship curve: shows the number or proportion of members of a cohort still alive at each age - Reproductive table: gives the age-specific reproduction rates in a population
Section 52.2:Life History
Life Histories - Natural selection favors traits that improve an organism’s chances of survival and reproductive success. - In every species, there are trade-offs between survival and the necessary but risky behaviors such as reproduction, the number of offspring produced, and investment in parental care.
- The traits that affect an organism′s schedule of reproduction and survival (from birth through reproduction to death) make up its Life History.
Life history is made up by the traits that affect an organism’s schedule of reproduction and survival. - Life histories are highly diverse, but they also exhibit patterns. - Life histories entail three basic variables: when reproduction begins, how often the organism reproduces, and how many offspring are produced during each reproductive episode. - Life history traits are results of evolutionary changes reflected in the physiology, and behavior of an organism.
Big-Bang Reproduction, also known as Semelparity, is when an individual produces a large number of offspring and then dies. - An example of this is the Agave plant. - Repeated Reproduction, also known as Iteroparity, is the opposite of this, where organisms produce only a few offspring during episodes. - What factors contribute to the evolution of semelparity and iteroparity? How much does an individual gain in reproductive success through one pattern versus the other? - The critical factor is the survival rate of the offspring.
- Big-bang reproduction (semelparity) is favored when the survival of offspring is low, as in highly variable or unpredictable environments. - Repeated reproduction (iteroparity) is favored in dependable environments where competition for resources is intense. - In such environments, a few, well-provisioned offspring have a better chance of surviving to reproductive age.
Limited resources mandate trade-offs between investment in reproduction and survival. In the real world, organisms have limited resources, and limited resources mean trade-offs between their needs for survival and reproduction.
Life histories represent an evolutionary resolution of several conflicting demands. - Sometimes we see trade-offs between survival and reproduction when resources are limited. - For example, red deer females have a higher mortality rate in winters following summers in which they reproduce because of the strain this puts on them.
Selective pressures also influence the trade-off between number and size of offspring. - Plants and animals whose young are subject to high mortality rates often produce large numbers of relatively small offspring. - Plants that colonize environments prone to changing usually produce many small seeds, only a few of which reach suitable habitat. - Smaller seed size may increase the chance of seedling establishment by enabling seeds to be carried longer distances to a broader range of habitats.
In other organisms, extra investment on the part of the parent greatly increases the offspring’s chances of survival. - An example of this is that oak, walnut, and coconut trees all have large seeds with a large store of energy and nutrients to help the seedlings become established. - In animals, parental care does not always end after incubation or gestation. - Primates provide an extended period of parental care.
Section 52.3: 52.3 Population Growth The exponential model of population (hypothetical population) ---- population growth in an idealized, unlimited environment. · unlimited population increase does not occur indefinitely for any species, either in the laboratory or in nature. · Ideal condition: Change in population size =Births - Deaths during time interval
Next, we can convert this simple model into one in which births and deaths are expressed as the average number of births and deaths per individual during the specified time interval. The per capita birth rate is the number of offspring produced per unit time by an average member of the population.
· Population ecologists are most interested in the differences between the per capita birth rate and the per capita death rate ----- per capita rate of increase or r · The value of r indicates whether a population is growing (r > 0) or declining (r< 0). · If r = 0, then there is zero population growth (ZPG). ° Births and deaths still occur, but they balance exactly.
· Exponential population growth.(graph) ° Under these conditions, we may assume the maximum growth rate for the population (rmax), called the intrinsic rate of increase. · The size of a population that is growing exponentially increases at a constant rate, resulting in a J-shaped growth curve when the population size is plotted over time. ° Although the intrinsic rate of increase is constant, the population accumulates more new individuals per unit of time when it is large. ° As a result, the curve gets steeper over time. · A population with a high intrinsic rate of increase grows faster than one with a lower rate of increase. J-shaped curves are characteristic of populations that are introduced into a new or unfilled environment or whose numbers have been drastically reduced by a catastrophic event and are rebounding.
Section 52.4:The Logistic Growth Model Carrying capacity: the maximum population size that a particular environment can support Logistic population growth: the per capita rate of increase declines as carrying capacity is reached [Insert Figures 52.11 & 52.12 here]
K-selection: selection for life history traits that are sensitive to population density. vs. R-selection: selection for life history traits that maximize reproductive success in uncrowded environments [Insert Figure 52.13]
52.5:Populations are regulated by complex interaction of biotic and abiotic influences. [Review: What are biotic / abiotic? Biotic = living organisms in an environment. Abiotic = chemical/physical factors in an environment.]
Population Change / Density - If a population density changes while the birth and death rate DON’T, then it is density independent. - If a population density increases while the birth rate FALLS and the death rate RISES, then it is density dependent. If both death and birth rates are density dependent, then a population can reach an equilibrium density.
Density-Dependent Population Regulation Density-dependent decreases in birth rate and increases in death rate can regulate populations through negative feedback. Environmental and territorial factors can affect the birth and death rates: Competition for resources Territoriality Health Predation Toxic Wastes Insintric Factors
Population Dynamics Population dynamics: studies the variations in population size and what factors cause them. [eg. The decrease in grazers’ population during the winter is due to the severity of the winter climate]. In some cases, some populations can form a metapopulation in which immigration and emigration may significantly influence individual population sizes.
Population Cycles Population cycles are studied to show how some factors affect how certain species survive within a certain population [eg. Studying the density of snowshoe hares in forests to determine whether food shortages, predator overexploitation, or both cause the collapse in hare populations).
52.6:Human Population Growth has Slowed after Centuries of Exponential Increase. The Global Human Population For centuries, the human population has grown continually, but now is slowing in growth. Demographic Transition: the model used to show the transition between high birth / death rates and low birth / death rates in certain societies. Age Structure: the distribution of various age groups in a human population (typically that of a country or region of the world). Infant Mortality and life expectancy at birth are factors that vary among certain human populations. [Insert Figure 52.25] (Know how to interpret this graph)
Global Carrying Capacity Ecological Footprint: Measures human needs in estimating carrying capacity [carrying capacity is the amount of human life that is estimated to be able to be supported on earth]. Ecological Capacities: resource bases of every nation station how each country’s peoples needs affect the ecological footprint
----------------------------------------------------CONGRATS! You finished Chapter 52!!!--------------------------------------------------------------
Identify three density–dependent factors that limit population size, and explain how each exerts negative feedback.
Population: a group of individuals of a single species living in the same general area
Population ecology: the study of populations and how the environment influences that population’s density, distribution, size, and age structure.
Section 52.1: Dynamic Biological Processes influence population’s density, dispersion, and demography
Density [number of individuals per capita]
(Eg: number of oak trees per kilometer)
- Mark-recapture method: captured animals are marked with tags, collars, bands, or spots of dyes, and then released; after a few days or weeks, traps are set again; the second capture yields both marked and unmarked individuals.
Data yields researches to estimate the total number of individuals in the population.
Dispersion [How individuals space/pattern themselves in a certain population]
- Immigration: an influx of organisms entering a certain environment
- Emigration: an influx of organisms leaving a certain environment
- Territoriality: the defense of a physical space
[Insert figure 52.3 from textbook]
Demography [the study of vital statistics of a population]
- Life table: presents age-specific survival data for a population
- Survivorship curve: shows the number or proportion of members of a cohort still alive at each age
- Reproductive table: gives the age-specific reproduction rates in a population
Section 52.2: Life History
Life Histories
- Natural selection favors traits that improve an organism’s chances of survival and reproductive success.
- In every species, there are trade-offs between survival and the necessary but risky behaviors such as reproduction, the number of offspring produced, and investment in parental care.
- The traits that affect an organism′s schedule of reproduction and survival (from birth through reproduction to death) make up its Life History.
Life history is made up by the traits that affect an organism’s schedule of reproduction and survival.
- Life histories are highly diverse, but they also exhibit patterns.
- Life histories entail three basic variables: when reproduction begins, how often the organism reproduces, and how many offspring are produced during each reproductive episode.
- Life history traits are results of evolutionary changes reflected in the physiology, and behavior of an organism.
Big-Bang Reproduction, also known as Semelparity, is when an individual produces a large number of offspring and then dies.
- An example of this is the Agave plant.
- Repeated Reproduction, also known as Iteroparity, is the opposite of this, where organisms produce only a few offspring during episodes.
- What factors contribute to the evolution of semelparity and iteroparity? How much does an individual gain in reproductive success through one pattern versus the other?
- The critical factor is the survival rate of the offspring.
- Big-bang reproduction (semelparity) is favored when the survival of offspring is low, as in highly variable or unpredictable environments.
- Repeated reproduction (iteroparity) is favored in dependable environments where competition for resources is intense.
- In such environments, a few, well-provisioned offspring have a better chance of surviving to reproductive age.
Limited resources mandate trade-offs between investment in reproduction and survival.
In the real world, organisms have limited resources, and limited resources mean trade-offs between their needs for survival and reproduction.
Life histories represent an evolutionary resolution of several conflicting demands.
- Sometimes we see trade-offs between survival and reproduction when resources are limited.
- For example, red deer females have a higher mortality rate in winters following summers in which they reproduce because of the strain this puts on them.
Selective pressures also influence the trade-off between number and size of offspring.
- Plants and animals whose young are subject to high mortality rates often produce large numbers of relatively small offspring.
- Plants that colonize environments prone to changing usually produce many small seeds, only a few of which reach suitable habitat.
- Smaller seed size may increase the chance of seedling establishment by enabling seeds to be carried longer distances to a broader range of habitats.
In other organisms, extra investment on the part of the parent greatly increases the offspring’s chances of survival.
- An example of this is that oak, walnut, and coconut trees all have large seeds with a large store of energy and nutrients to help the seedlings become established.
- In animals, parental care does not always end after incubation or gestation.
- Primates provide an extended period of parental care.
Section 52.3:
52.3 Population Growth
The exponential model of population (hypothetical population) ---- population growth in an idealized, unlimited environment.
· unlimited population increase does not occur indefinitely for any species, either in the laboratory or in nature.
· Ideal condition:
Change in population size =Births - Deaths
during time interval
Next, we can convert this simple model into one in which births and deaths are expressed as the average number of births and deaths per individual during the specified time interval.
The per capita birth rate is the number of offspring produced per unit time by an average member of the population.
· Population ecologists are most interested in the differences between the per capita birth rate and the per capita death rate ----- per capita rate of increase or r
· The value of r indicates whether a population is growing (r > 0) or declining (r < 0).
· If r = 0, then there is zero population growth (ZPG).
° Births and deaths still occur, but they balance exactly.
· Exponential population growth.(graph)
° Under these conditions, we may assume the maximum growth rate for the population (rmax), called the intrinsic rate of increase.
· The size of a population that is growing exponentially increases at a constant rate, resulting in a J-shaped growth curve when the population size is plotted over time.
° Although the intrinsic rate of increase is constant, the population accumulates more new individuals per unit of time when it is large.
° As a result, the curve gets steeper over time.
· A population with a high intrinsic rate of increase grows faster than one with a lower rate of increase.
J-shaped curves are characteristic of populations that are introduced into a new or unfilled environment or whose numbers have been drastically reduced by a catastrophic event and are rebounding.
Section 52.4:The Logistic Growth Model
Carrying capacity: the maximum population size that a particular environment can support
Logistic population growth: the per capita rate of increase declines as carrying capacity is reached
[Insert Figures 52.11 & 52.12 here]
K-selection: selection for life history traits that are sensitive to population density.
vs.
R-selection: selection for life history traits that maximize reproductive success in uncrowded environments
[Insert Figure 52.13]
52.5: Populations are regulated by complex interaction of biotic and abiotic influences.
[Review: What are biotic / abiotic? Biotic = living organisms in an environment. Abiotic = chemical/physical factors in an environment.]
Population Change / Density
- If a population density changes while the birth and death rate DON’T, then it is density independent.
- If a population density increases while the birth rate FALLS and the death rate RISES, then it is density dependent.
If both death and birth rates are density dependent, then a population can reach an equilibrium density.
Density-Dependent Population Regulation
Density-dependent decreases in birth rate and increases in death rate can regulate populations through negative feedback. Environmental and territorial factors can affect the birth and death rates:
Competition for resources
Territoriality
Health
Predation
Toxic Wastes
Insintric Factors
Population Dynamics
Population dynamics: studies the variations in population size and what factors cause them. [eg. The decrease in grazers’ population during the winter is due to the severity of the winter climate].
In some cases, some populations can form a metapopulation in which immigration and emigration may significantly influence individual population sizes.
Population Cycles
Population cycles are studied to show how some factors affect how certain species survive within a certain population [eg. Studying the density of snowshoe hares in forests to determine whether food shortages, predator overexploitation, or both cause the collapse in hare populations).
52.6: Human Population Growth has Slowed after Centuries of Exponential Increase.
The Global Human Population
For centuries, the human population has grown continually, but now is slowing in growth.
Demographic Transition: the model used to show the transition between high birth / death rates and low birth / death rates in certain societies.
Age Structure: the distribution of various age groups in a human population (typically that of a country or region of the world).
Infant Mortality and life expectancy at birth are factors that vary among certain human populations.
[Insert Figure 52.25]
(Know how to interpret this graph)
Global Carrying Capacity
Ecological Footprint: Measures human needs in estimating carrying capacity [carrying capacity is the amount of human life that is estimated to be able to be supported on earth].
Ecological Capacities: resource bases of every nation station how each country’s peoples needs affect the ecological footprint
----------------------------------------------------CONGRATS! You finished Chapter 52!!!--------------------------------------------------------------
Identify three density–dependent factors that limit population size, and explain how each exerts negative feedback.